ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
ISSN-L : 0915-1559
Effects of Tramp Elements on Formability of Low-carbon TRIP-aided Multiphase Cold-rolled Steel Sheets
Chang Gil LeeSung-Joon KimTae-Ho LeeChang-Seok Oh
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2004 Volume 44 Issue 4 Pages 737-743

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Abstract

Four kinds of TRIP-aided cold-rolled steel sheets were fabricated with additions of tramp elements of Cu, Cr, and Ni to a basic 0.15C-1.5Mn-1.5Si-0.5Cu (hereafter all in wt%) steel, and their microstructures, mechanical properties, and formability were investigated to analyze the effects of the addition of tramp elements. These steel sheets were intercritically annealed at 780-790°C, and isothermally treated at 430°C. Tensile tests and limiting dome height (LDH) tests were conducted, and the changes of retained austenite volume fractions as a function of tensile strain were measured using X-ray diffraction. The formability of the Cu- and Ni-containing cold-rolled steel sheets was greatly improved as the strain-induced transformation of retained austenite was sustained up to the high strain region due to their high volume fraction and stability of retained austenite. On the other hand, the Cr-containing steel sheets showed a dual-phase structure of ferrite and martensite resulting from low volume fraction and stability of retained austenite and a large amount of transformed martensite. These findings indicated that when tramp elements such as Cu, Cr, and Ni were positively used, low-carbon TRIP-aided cold-rolled steel sheets having mechanical properties suitable for various application purposes and excellent formability could be successfully achieved.

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